1. Field of the Invention
The present invention relates to an electroacoustic transducer for generating sound by electromagnetic acoustic conversion, and a method for manufacturing such an electroacoustic transducer.
2. Description of the Related Art
An electroacoustic transducer has a magnetic circuit in which a magnetic field from a magnet passes through a base member, a magnetic core and a diaphragm and returns the magnet again. When an electric oscillating signal is supplied to a coil wound around the magnetic core, an oscillating magnetic field generated by the coil is superimposed on the magnetostatic field of the magnetic circuit so that oscillation generated in the diaphragm is transmitted to the air. Thus, sound is generated.
Various properties of the electroacoustic transducer, for example, the sound pressure level, the frequency characteristic, the conversion efficiency, etc. vary complicatedly in accordance with the materials, the parts dimensions, the assembly accuracy of the base member, the magnetic core, the diaphragm, the magnet, and so on. Particularly, the dimensional variation of an air gap between a forward end of the magnetic core and the diaphragm has a large influence on the distribution of a magnetic field acting on the diaphragm. Therefore, severe accuracy control is required for the air gap.
It is an object of the present invention to provide an electroacoustic transducer in which the positional accuracy of members can be improved on a large scale and stable properties can be obtained, and to provide a method for manufacturing such an electroacoustic transducer.
According to the present invention, there is provided an electroacoustic transducer comprising: a plate-like base member formed of magnetic material; a magnetic core formed of magnetic material and provided erectly on the base member; a diaphragm formed of magnetic material and supported with an air gap between the diaphragm and a forward end of the magnetic core; a magnet constituting a magnetic circuit together with the base member, the magnetic core and the diaphragm so as to provide a magnetostatic field; a coil disposed around the magnetic core for applying an oscillating magnetic field to the magnetic circuit; and a housing member molded integrally with the base member and the magnet, the housing member having a notch portion extending from a bottom surface thereof to the magnet.
According to the present invention, because the housing member has a notch portion extending from a bottom surface thereof to the magnet, the magnet is exposed through the notch portion so that access to the magnet can be made from the outside. Accordingly, quality control such as positioning or position-measuring of the magnet, or the like, can be carried out in a step of assembling or inspecting the electroacoustic transducer. Thus, it is possible to realize an electroacoustic transducer having stable properties.
In addition, the present invention has a feature that the notch portion is filled with a filler.
According to the present invention, though there is no problem in operation even if the notch portion of the housing member is left as it is, air tightness, durability, and so on, of products can be enhanced by filling the notch portion with a filer of synthetic resin or the like.
In addition, the present invention has a feature that a pedestal for supporting the diaphragm is formed on the housing member.
According to the present invention, because the attachment accuracy of the diaphragm to the housing member is improved by forming the pedestal to support the diaphragm on the housing member, the size of the air gap between the diaphragm and the forward end of the magnetic core can be kept with high accuracy.
Further, according to the present invention, there is provided a method for manufacturing an electroacoustic transducer, wherein the transducer comprises: a plate-like base member formed of magnetic material; a magnetic core formed of magnetic material and provided erectly on the base member; a diaphragm formed of magnetic material and supported with an air gap between the diaphragm and a forward end of the magnetic core; a magnet constituting a magnetic circuit together with the base member, the magnetic core and the diaphragm so as to provide a magnetostatic field; a coil disposed around the magnetic core for applying an oscillating magnetic field to the magnetic circuit; and a housing member molded integrally with the base member and the magnet; and wherein the method for manufacturing the electroacoustic transducer comprises the steps of: inserting the base member and the magnet into a mold; and injecting synthetic resin into the mold in a condition that a pressing pin provided in the mold presses the magnet from the base member side to thereby insert-mold the housing member.
According to the present invention, in the case where the housing member is insert-molded together with the base member and the magnet, a pressing pin for positioning the magnet is provided in a mold, and synthetic resin is injected in a condition that the pressing pin presses the magnet from the base member side. Accordingly, when the synthetic resin flows into a gap between the base member and the magnet, the magnet can be prevented from floating or shifting in position. Thus, an adequate quantity of synthetic resin can be poured into this gap. In addition, because an adequate quantity of synthetic resin enters the gap, the resin injection pressure distribution or the stress distribution at the time of resin solidification becomes uniform all over the resin. Thus, it is possible to prevent the base member from being deformed due to uneven pressure, so that it is possible to improve the positional accuracy of the members constituting the magnetic circuit on a large scale. Particularly, it is possible to keep the size of the air gap between the forward end of the magnetic core and the diaphragm with high precision.
In addition, it is preferable that the pressing pin is removably attached to the mold so that the pressing pin can be replaced with another pressing pin having a different regulating position even if the thickness of the magnet is changed in accordance with product specifications.
In addition, the present invention has a feature that the method further comprises the step of filling a notch portion of the housing member formed by the pressing pin with a filler.
According to the present invention, though there is no problem in operation even if the notch portion of the housing member is left as it is, air tightness, durability, and so on, of products can be enhanced by filling the notch portion with a filer of synthetic resin or the like.